This invention relates generally to sensors and as an example of their use this specification describes security apparatus and in particular various types of sensors used to determine whether a predetermined condition exists and whether that condition should trigger an appropriate response in the context of a security environment.
In one example of a single sensor security apparatus, a passive infrared (PIR) detector sensor is used to sense the presence of a heat radiating body (typically an unauthorized person) in its field of view. In a further example of a single sensor used in a security environment a video camera can provide both a visual indication of the presence of a body (also typically an unauthorised person) in its field of view, and motion detection by analysing the time changing video signal.
It is known for a single sensor to provide a signal which when suitably processed and compared with a predetermined condition can indicate for example the presence of an unauthorised person but it is also likely to detect other effects (e.g. air disturbance, heating, small animals, etc) which may also match predetermined conditions and inappropriate responses may occur as a result,
Surveillance systems which use very broadly defined predetermined conditions often falsely trigger. However on the other hand very narrowly defined predetermined conditions may only trigger a response when obvious intrusions into an area occur which risk missing a less obvious but equally potentially damaging intrusion into the area within the field of view of the single sensor.
Both extremes are undesirable,
It is also known to use quite sophisticated predetermined conditions which are designed to tailor the various intrusion conditions to the characteristics of the sensor and lessen the likelihood of false triggering.
In one example, it is known to electronically process the output of a PIR sensor to enhance those signals that will improve the determination of whether there exists a heat radiating body of a particular type. Those signals can also be enhanced so that the rate of movement of the intruder through the field of view of the PIR sensor can be determined. Thus, it is possible, using these enhanced signals to met predetermined conditions which more reliably define the trigger for an appropriate response.
In a further example, it is also known as discussed previously, to process the output of a video camera to provide a time related indication of the past movement of a body through its field of view.
It is typical for each of the abovementioned types of sensors to be used individually each having their own different predetermined characteristics which must be met before triggering an appropriate response. These sensors and their processed outputs are then further processed in a logical but serial fashion. It is likely therefore that if both sensors are triggered by an appropriate predetermined characteristic an intrusion situation has been correctly determined. It however only one of the sensors is triggered there is uncertainty in the determination and a greater likelihood of false triggering.
The invention to be described uses two quite different sensors using disparate portions of the electromagnetic spectrum to be matched, for example using the lowest resolution sensor (eg a PIR) as the map for zoning of the highest resolution sensor (eg high resolution CCD video).
In one example of the prior uses of two different types of sensors, a PIR sensor is mounted near the ceiling in a corner of a room opposite a doorway, and a video camera is mounted over the doorway pointing towards the interior of the room. In this example, the fields of view of each sensor partially overlap and may be used to support the operation of the other. However, it is believed by the inventor that this approach can only be useful if it is known how the sensor fields actually overlap and the predetermined characteristics of each sensor are interrelated in a reliable and coordinated manner.
In another example, a PIR sensor mounted near the ceiling in a corner of a room, and a video camera mounted adjacent to it, are both directed towards the center of the room with only a portion of their fields of view overlapping.
It is known to use one and then other output signals from these two different type of sensors. However, there does not appear to exist any evidence of the combination of their output signals or any evidence of the adaption of the output signals of one sensor to mimic one or more of the characteristics or output signals of the other, so that the sensor signals can be further co-processed using data fusion techniques to determine whether one of a set of sensor interdependent predetermined conditions is matched.
Furthermore the inventor has determined that matched portions of the field of view of each sensor can be processed in a manner that optimises the relevance of the signals detected and which can together more positively identify intrusions into the field of view of the sensors and in particular the matched portions of their field of view.
Therefore, it is an aspect of the invention to provide an arrangement of sensors having at least one of their characteristics such as for example their fields of view, processed such that the operation of one sensor can be interrelated with the operation of the other and so that the predetermined condition required to trigger an appropriate response is determined so as to account for the matched portions of their field of view and the matched characteristic of the sensors.
Sensor arrangements having matched spatial reception and detection characteristics as well as matched portions of their field of view, such as fox example setting up the same fields of view and/or aspect ratios will enable the use of very sophisticated predetermined conditions and data fusion to improve the likelihood of reliable triggering of the surveillance system.